Our preliminary studies in early weaned (15 d/o) neonatal rats showed the induction of proximal small intestinal and pancreatic ornithine decarboxylase (ODC) activities. The induction of ODC was 1-2 day earlier than the precocious expression of proximal showed for the first time the ontogeny of intestinal tyrosine kinases (Tyr-k) with parallelism between Tyr-k and growth and maturation of the rat small intestine. The overall aim of the current Grant Proposal is to define, at the cellular and gene expression level, the effect of early weaning on small intestinal and pancreatic development in neonatal rats. We will examine the role of these two proliferative enzymes-ODC and Tyr-K in the development of small intestine and pancreas after early weaning. Specifically we will: 1) Evaluate the growth and development parameters of small intestine and pancreas after early weaning and its relationship with ODC and Tyr-k. 2) Examine the essential roles of ODC and Tyr-K in the development of small intestine and pancreas after early weaning by administration of its respective inhibitor and assess the resultant effects of the development of these two organs. 3) Study (i) gene expression of ODC, Tyr-k (EGF-R Tyr-k and pp60c-src Tyr-k of small intestine, after early weaning. The findings from current proposed studies will enable us to understand the intracellular events and its regulatory mechanisms of developmental process of small intestine and pancreas in weaning and early weaning.